2) Superman Lives
Surely the most legendary of all unmade superhero movies is Superman Lives – the reboot of the character that was developed during the 90s. It famously had a lot of big names attached; from a script by Kevin Smith, it would have been directed by Tim Burton and starred Nicolas Cage as the Man of Steel.
Featuring Lex Luthor, Brainiac AND Doomsday as the villains, the movie would have focussed on the outsider aspect of Superman, something that Burton brought to the table. The film was in development for about five years on and off – with Cage even undergoing several costume fittings – before the film was shelved forever.
Basically, the failure of Superman Lives is the fault of too many cooks spoiling the broth, with Burton and Smith clashing with each other as well as the interfering studio. For those wondering what the movie would have been like, a documentary titled The Death of Superman Lives: What Happened? was released in 2015.